Conventional packaged devices are manufactured for specific performance characteristics required for use in a wide range of electronic equipment. Packaged microelectronic devices typically include a die with integrated circuitry, a casing encapsulating the die, and an array of external contacts. Packaged microelectronic devices have an outer shape that defines a package profile. The external contacts can be pin-like leads or ball-pads of a ball-grid array. The ball-pads are arranged in a selected pattern, and solder balls are connected to the ball-pads. Different types of packaged devices with different circuitry can have the same ball-grid array but different outer profiles.
After the dies are packaged, the devices are generally tested and marked in several post-production batch processes. Burn-in testing is one such post-production process for detecting whether any of the devices are likely to fail. Burn-in testing is performed before shipping packaged devices to customers or installing packaged devices in electronic equipment.
Burn-in testing of packaged devices typically involves applying specified electrical biases and signals to the pins or ball-pads of the devices in a controlled temperature environment. The packaged devices are generally tested in more severe conditions and/or under more rigorous performance parameters than they are likely to experience during normal operation. During a typical burn-in test, several packaged devices are loaded onto burn-in boards, and a batch of loaded burn-in boards is then placed in a test chamber (i.e., burn-in oven) that provides a controlled environment.
Burn-in boards are commonly printed circuit boards that conduct the electrical input/output signals to the packaged devices. One example of a conventional burn-in board includes a printed circuit board and a plurality of test sockets on the printed circuit board. The test sockets each have a selected array of electrical leads electrically coupled to conductive lines in the printed circuit board. The electrical leads also have exposed contact tips positioned to engage solder balls of a packaged microelectronic device loaded into the socket.
Burn-in boards also have fuses to protect the circuitry in the test sockets from overloading, and other passive components can be attached to burn-in boards to control the electrical parameters at the sockets. FIG. 1 is a schematic side cross-sectional view of a burn-in board 10 having a primary side 12 with a test site 13 and a secondary side 14. The burn-in board 10 further includes a socket 15 at the test site 13 and a chip-fuse 16 attached to the secondary side 14 using surface mounting technology. The chip-fuse 16 has a first contact 17 and a second contact 18 electrically coupled to circuitry 19 associated with the test site 13. The burn-in board 10 can further include a plurality of holes 20 for receiving a fuse or other type of passive component that operates with the test site 13. Each hole 20 can have a sidewall covered by a plated section 22, and the burn-in board 10 can further include circuitry 26 that electrically couples the plated sections 22 to the test site 13. Burn-in boards generally have several hundred test sites that each have a socket, chip-fuse, and replacement holes. In conventional burn-in boards, fuse sockets 28 are soldered to the plated sections 22 in the holes 20 at each test site to receive a replacement fuse or other type of passive component.
Burn-in tests can cause a microdevice to overload and blow the chip-fuse 16 at the test site 13. In such cases, an axial-type replacement fuse 30 is generally inserted into the fuse sockets 28 so that the test site 13 can be used to test more devices. Conventional replacement fuses typically have a first lead 32, a second lead 34, and a fuse element 36 coupled to the first and second leads 32 and 34. The replacement lead 30 is passed between adjacent sockets 15 until the first lead 32 is received in a first fuse socket 28 and the second lead 34 is received in a second fuse socket 28. The test site 13 may then be used for testing additional devices even though the chip-fuse 16 is no longer operational.
One disadvantage of the conventional burn-in board 10 illustrated in FIG. 1 is that it is relatively expensive to assemble. When the burn-in board 10 is initially assembled, all of the fuse sockets 28 are attached to the primary side 12 because it is difficult to access the primary side 12 after the sockets 15 have been mounted to the board 10. Typical burn-in boards have hundreds of test sites, and thus it is time consuming to insert and solder each of the fuse sockets 28 to the holes 20. The cost of the fuse sockets 28 also increases the cost of the burn-in board 10. Moreover, many of the fuse sockets 28 are never used because many of the chip-fuses never blow during the life of the board 10. As a result, it is costly to assemble burn-in boards to accommodate axial-type replacement fuses 30.
Another disadvantage of the conventional burn-in board 10 illustrated in FIG. 1 is that the fuse sockets 28 are fairly large and occupy routing space between test sites 13. The electronics industry continuously pushes for smaller and higher performance devices, and thus the burn-in boards 10 must be able to accommodate microelectronic devices with more input/output pins. As a result, the space occupied by the fuse sockets 28 can limit whether the burn-in boards can be used to test high-performance devices.
Another disadvantage of the conventional burn-in board 10 illustrated in FIG. 1 is that the axial-type replacement fuse 30 may not have the same electrical properties as the chip-fuse 16. As a result, when the chip-fuse 16 blows, the test site 13 may need to be recalibrated after the replacement fuse 30 is installed. This requires additional time that increases the cost and reduces the throughput of operating the burn-in board 10.